The overall goals of this research are to understand in more detail the molecular basis for the restricted specificity of human alpha-thrombin by identifying and mapping thrombin active site binding regions involved in catalytic specificity and biological recognition. In particular, mapping-topography studies of human thrombins will be carried out in order to determine distances, overlaps and structural links between various active site loci. Of particularly critical importance will be the pursuit of structural information pertaining to the coagulant ability of thrombin. We have available for study, also, gamma-thrombin, a non-coagulant thrombin. Structural comparisons between alpha- and gamma-thrombin serve as excellent experimental control systems for examining specifically binding site interactions. The experimental approaches will involve electron spin resonance (spin labels), nuclear magnetic resonance, fluorescence spectroscopy and general kinetic and enzymological approaches.